A droplet actuator typically includes one or more substrates configured to form a surface or gap for conducting droplet operations. The one or more substrates establish the droplet operations surface or gap and may also include electrodes arrange to conduct the droplet operations. The droplet operations substrate or the gap between the substrates is typically coated or filled with a filler fluid that is immiscible with the liquid that forms the droplets.
Droplet actuators are used in a variety of applications, including molecular diagnostic assays, such as quantitative polymerase chain reaction (qPCR) and immunoassays. Molecular diagnostic assays are used in a wide variety of settings, such as infectious pathogen detection and point-of-care diagnosis. Current microfluidic protocols for sample preparation typically begin with analyte capture beads suspended in a small volume (e.g., 250 microliters (μL)) of lysed sample. Individual droplets are then dispensed and the capture beads are concentrated in a single droplet over a permanent magnet. However, bead dispensing, concentrating, and washing are time-consuming steps and significantly increase the time-to-result of a diagnostic assay. Consequently, new approaches are needed to achieve rapid “sample-to-result” molecular diagnostics for point-of-care use.